Does aluminum wire need to be thicker than copper?

[ohwilleke]

Does an aluminum wire have any performance disadvantages other than having to be thicker to carry the same amount of current?

 

[Astronuc]

The principal advantage is the mass per unit length (low denisty) and the cost.

http://www.metalprices.com/ - Al has recently fallen to about $0.80/lb from $0.90/lb, while copper varies between $1.45-1.50/lb.

Another advantage is corrosion resistance. Aluminum forms a tougher, more protective oxide than copper.

 

[ohwilleke]

I'm not worried about cost. I've been thinking about how you would manage economically in a copper and silver scarce environment, and in that environment, copper would be much more expensive than aluminium.

 

[Oleh Iwanusiw]

Obviously youall have not heard that there was a time when aluminium wiring was used in himes and elsewhere. This practice was stopped - not by a law or UL directive, but by the spread of the WORD . . that the %$#@&$ aluminium wiring was no damn good.

Unlike other metals - pure aluminium (the one that has to used for wiring) "flows under load" (deforms) . . . this causes poor contacts . . . which deteriorate further as they get hotter . . .
Aluminium does form an "oxide layer" that protects the wire - but causes connection problems. Thus aluminium wiring MUST be used with special fittings in order to avoid all these pitfalls.

Oleh

 

[Astronuc]

Obviously youall have not heard that there was a time when aluminium wiring was used in himes and elsewhere. This practice was stopped - not by a law or UL directive, but by the spread of the WORD . . that the %$#@&$ aluminium wiring was no damn good.

Unlike other metals - pure aluminium (the one that has to used for wiring) "flows under load" (deforms) . . . this causes poor contacts . . . which deteriorate further as they get hotter . . .
Aluminium does form an "oxide layer" that protects the wire - but causes connection problems. Thus aluminium wiring MUST be used with special fittings in order to avoid all these pitfalls.

Actually I have heard about that. Al has a much higher coefficient of thermal expansion (CTE) (Al 25 x 10^-6 °C^-1 at RT) than most of the materials used as standard connectors and compared to copper (CTE = 16.6 x 10^-6 °C^-1 at RT), and yes, one needs special fittings to avoid the problem. Since Al expands, it would be under compression in the fitting, and as it flows under compression, it deforms (flows) as stated by Oleh. IIRC, Al is also softer than copper, for a given amount of cold-work.

Back in the 60's ALCO Locomotive Company decided to save big bucks on their locomotive by using Al wiring, and these are big wires for high amps. It was a disaster! Due to the phenomenon stated, connections deteriorated and fires resulted. That was one of the contributing factors to their bankruptcy.

 

[Rogue Physicist]

Another factor which hasn't been mentioned here is that it is a bad choice for other reasons: Somewhere along the line connectors, fasteners, destination and source linkages must usually or at least will be made from other metals like copper, brass, steel etc.

Another big fire-starter/corrosion problem is at the point of junction between dissimilar metals, especially carrying current. In fact, aluminium wiring *is* banned in Canada and other intelligent countries. Wherever found it must be ripped out or made impossible to re-connect to house or building wiring to prevent fires and qualify for fire insurance.

Wherever you intend to use it, it would be irresponsible if not illegal to do so without taking extra (and expensive) precautions to prevent fires or eliminate risks from failure. So it is *not* cheaper.

And nothing is less expensive than preventing fire, property damage and death, unless that is your actual goal.

 

[chriskt]

This discussion is hilarious, too bad I wasn't aware of it when it was ongoing. Aluminum wire has not been outlawed in Canada or the U.S.-check the Canadian Electrical Code and the National Electerical Code. Aluminum wire is installed in millions of circuits every year, and the connections were changed in the 1970s to ensure that the old problems did not occur again. If you want real information on what happened, go to http://magazine.iaei.org/magazine/06_a/hunter.html